Volvo XC90 Owner's Manual page 216

CLIMATE CONTROL
Air distribution options
Air distribution can be adjusted manually if nee-
ded. The following options are available.
Air distribution
If all air distribution buttons are deselected in manual mode, the climate control system will revert to automatic mode.
Main airflow from defroster vents. Some airflow from other vents.
Main airflow from dashboard vents. Some airflow from other vents.
Main airflow from floor vents. Some airflow from other vents.
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Purpose
Helps remove ice and condensation in cold and humid weather
(blower speed should not be set too low).
Provides effective cooling in warm weather.
Provides heating or cooling in footwell areas.